Electrolyte for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings and removing method using same

ABSTRACT

An electrolyte for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings from substrates, the electrolyte includes an acid, an inhibiter and a complexant. The acid is a mixture of a sulfuric acid and a weak acid. The inhibiter is an organic compound containing hydrophilic group, lipophilic group, and at least one polar group selected from nitrogen-containing group, sulfur-containing group, and hydroxyl group. The complexant is capable of complexing with Fe 3+ . A method for removing the metal-carbide/nitride coatings or metal-carbide-nitride coatings using the electrolyte is also provided.

BACKGROUND

1. Technical Field

The exemplary disclosure relates to an electrolyte for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings and removing method using the electrolyte.

2. Description of Related Art

Hard coatings, such as metal-carbide/nitride coatings or metal-carbide-nitride coatings, impart specific properties to workpieces such as machining tools, die core-pins, and high temperature devices. These hard coatings resist wear, abrasion, oxidation, and corrosion, and reduce susceptibility to chemical reactions with the workpieces to which they are applied. These coatings, however, can fail locally during manufacture or use.

When the coatings fail, the entire die or tool component is discarded even if the underlying substrate shows no damage, at considerable cost. For this reason, the ability to recycle the underlying substrate by removing a failed coating and replacing it with a new coating is economically preferable.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION

The present disclosure relates to an electrolyte and a related method for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings formed on the surfaces of substrates. The substrate may be made of stainless steel or ferric-based alloy.

The electrolyte is an aqueous solution containing acid, inhibiter, complexant, and accelerant.

The acid is a mixture of a sulfuric acid and a weak acid. The acid provides an acid condition for changing the metal elements contained in the coatings into metal ions during electrolysis process. In the embodiment, the weak acid is oxalic acid or acetic acid. In the electrolyte, the mass percentage of the oxalic acid is about 3% to about 5%, the mass percentage of the acetic acid is about 1% to about 3%.

The inhibiter is an organic compound containing hydrophilic group, lipophilic group, and at least one polar group selected from nitrogen-containing group, sulfur-containing group, and hydroxyl group. The inhibiter is at least one selected from nicotinamide (C₆H₆N₂O), (N,N-methylenebis N′-1-(hydroxymethyl)-2,5-dioxo-4-imidazolidinyl))-urea (C₁₁H₁₆N₂O₈), and thiourea (H₄N)₂S). In the exemplary embodiment, a combination of C₆H₆N₂O and C₁₁H₁₆N₈O₈ may be selected. In the electrolyte, the concentration of the nicotinamide is about 0.1 g/l to about 0.3 g/l, and the concentration of the C₁₁H₁₆N₈O₈ is about 0.1 g/l to about 0.3 g/l. The inhibiter protects the substrate from being etched or damaged by the acid.

During the removing method, the inhibiter reduces the surface energy of the substrate, and enhances the activation energy for reaction, thus slowing down the corrosion rate of the electrolyte to the substrate. Furthermore, the polar group of the inhibiter can be electrostatic adsorbed onto the surface of the substrate to form a lipophilic layer on the surface of the substrate, which protects the substrate from being etched or damaged by the acid.

The complexant is capable of complexing with Fe³⁺, which inhibits the corrosion reaction that may exist on the surface of the substrate. The complexant is edetic acid (EDTA). In the electrolyte, the concentration of EDTA is about 0.1 g/l to about 0.2 g/l.

The accelerant is sodium dodecyl sulphonate (OP-10). In the electrolyte, the concentration of the OP-10 is about 0.1 g/l-0.2 g/l.

The electrolyte may be manufactured by dissolving the acid, inhibiter, complexant, and accelerant in water.

A method for removing the metal-carbide/nitride coatings or metal-carbide-nitride coatings using the electrolyte may at least include the following steps:

A substrate is provided. The substrate may be made of stainless steel or ferric-based alloy. At least one coating is formed on the substrate. The coating may be a metal-carbide coating, a metal-nitride coating, or a metal-carbide-nitride coating, metal-carbide/nitride coatings or metal-carbide-nitride coatings.

The electrolyte is provided. The substrate having the coating is immersed in the electrolyte and used as an anode, and carbon material may be provided and used as a cathode. The temperature of the electrolyte during electrolysis is room temperature. The current density is about 0.8 A/dm²-2 A/dm², the voltage is about 1 V-5 V. The electrolysis takes about 2 min-8 min. Then, the substrate is taken out of the electrolyte and rinsed with water and then dried.

After electrolysis, the coating can be effectively removed from the substrate and the underlying substrate is free from damage for the protection of the inhibiter and the accelerant.

EXAMPLES

Experimental examples of the present disclosure follow:

Example 1

0.1 g C₆H₆N₂O, 0.3 g C₁₁H₁₆N₈O₈, 0.1 g EDTA, 0.2 g OP-10, 5 ml oxalic acid, and 2 ml sulfuric acid were added to deionized water to produce 1000 ml of electrolyte.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had chromium nitride coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 4 min at an electric current density of about 1.4 A/dm² and an electrolysis voltage of about 3 V. After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water. There was no damage to the stainless steel substrate.

Example 2

0.3 g C₆H₆N₂O, 0.1 g C₁₁H₁₆N₈O₈, 0.2 g EDTA, 0.2 g OP-10, 5 ml oxalic acid, and 2 ml sulfuric acid were added to deionized water to produce 1000 ml of electrolyte.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had chromium carbide coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 4 min at an electric current density of about 1.4 A/dm² and an electrolysis voltage of about 3 V. After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water. There was no damage to the stainless steel substrate.

Example 3

0.3 g C₆H₆N₂O, 0.1 g C₁₁H₁₆N₈O₈, 0.2 g EDTA, 0.2 g OP-10, 5 ml acetic acid, and 2 ml sulfuric acid were added to deionized water to produce 1000 ml of electrolyte.

Samples of stainless steel substrate were provided. The stainless steel substrate samples had chromium carbide coatings formed thereon. The samples, being anodes, were completely immersed in the electrolyte for about 2 min at an electric current density of about 2 A/dm² and an electrolysis voltage of about 4V. After electrolysis, the samples were taken out of the electrolyte and were dried after being rinsed with water. There was no damage to the stainless steel substrate.

It is to be understood, however, that even through numerous characteristics and advantages of the exemplary disclosure have been set forth in the foregoing description, together with details of the system and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. An electrolyte for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings from substrates, the electrolyte comprising: an acid, the acid being a mixture of a sulfuric acid and a weak acid; an inhibiter, the inhibiter being an organic compound containing hydrophilic group, lipophilic group, and at least one polar group selected from nitrogen-containing group, sulfur-containing group, and hydroxyl group; and a complexant being capable of complexing with Fe³⁺.
 2. The electrolyte as claimed in claim 1, wherein the acid is a mixture of sulfuric acid and oxalic acid.
 3. The electrolyte as claimed in claim 2, wherein in the electrolyte, the mass percentage of the oxalic acid is about 3% to about 5%.
 4. The electrolyte as claimed in claim 1, wherein the acid is a mixture of sulfuric acid and acetic acid.
 5. The electrolyte as claimed in claim 4, wherein in the electrolyte, the mass percentage of the acetic acid is about 1%-3%.
 6. The electrolyte as claimed in claim 1, wherein the inhibiter is at least one selected from nicotinamide, (N,N-methylenebis N′-1-(hydroxymethyl)-2,5-dioxo-4-imidazolidinyl))-urea, and thiourea.
 7. The electrolyte as claimed in claim 1, wherein in the electrolyte, the concentration of the nicotinamide is about 0.1 g/l-0.3 g/l.
 8. The electrolyte as claimed in claim 6, wherein in the electrolyte, the concentration of the (N,N-methylenebis N′-1-(hydroxymethyl)-2,5-dioxo-4-imidazolidinyl))-urea is about 0.1 g/l to about 0.3 g/l.
 9. The electrolyte as claimed in claim 1, wherein the complexant is edetic acid.
 10. The electrolyte as claimed in claim 9, wherein in the electrolyte, the concentration of edetic acid is about 0.1 g/l to about 0.2 g/l.
 11. The electrolyte as claimed in claim 1, wherein the electrolyte further comprises accelerant, the accelerant is sodium dodecyl sulphonate.
 12. The electrolyte as claimed in claim 11, wherein in the electrolyte, the concentration of sodium dodecyl sulphonate is about 0.1 g/l to about 0.2 g/l.
 13. A method for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings comprising: providing a substrate having at least one coating formed thereon, the at least one coating being a metal-carbide coating, a metal-nitride coating, or a metal-carbide-nitride coating; manufacturing an electrolyte, the electrolyte comprising acid, inhibiter and complexant; immersing the substrate in the electrolyte to perform an electrolysis to remove the coating, the substrate being an anode; wherein the acid is a mixture of a sulfuric acid and a weak acid, the inhibiter being an organic compound containing hydrophilic group, lipophilic group, and at least one polar group selected from nitrogen-containing group, sulfur-containing group, and hydroxyl group; and the complexant is capable of complexing with Fe³⁺.
 14. The method as claimed in claim 13, wherein the substrate is made of stainless steel or ferric-based alloy.
 15. The method as claimed in claim 13, wherein the temperature of the electrolyte during electrolysis is room temperature.
 16. The method as claimed in claim 13, wherein during the electrolysis process, the current density is about 0.8 A/dm² to about 2 A/dm², the voltage is about 1 V to about 5 V, the electrolysis process takes about 2 min to about 8 min.
 17. The method as claimed in claim 13, wherein the acid is a mixture of sulfuric acid and oxalic acid.
 18. The method as claimed in claim 13, wherein the acid is a mixture of sulfuric acid and acetic acid.
 19. The method as claimed in claim 13, wherein the inhibiter is at least one selected from nicotinamide, (N,N-methylenebis N′-1-(hydroxymethyl)-2,5-dioxo-4-imidazolidinyl))-urea, and thiourea.
 20. The method as claimed in claim 13, wherein the complexant is edetic acid. 